This invention relates to a device and a method for measuring the dynamic pressure in the combustion chamber of, for example, a gas turbine machine.
As part of the monitoring controls and diagnostic tools for an operating combustion system in a rotary machine such as a gas turbine, it is necessary to measure and acquire various data including combustion chamber dynamic pressure. This data is used to confirm proper operational health of the combustion system, and is also used to tune the gas turbine engine so that it is operating with an appropriate balance between combustion dynamics and emissions. Measuring dynamic pressure directly in a combustion chamber requires a sensor that functions in operating environments having temperatures in the range of 2000-3000xc2x0 F. Currently, existing dynamic pressure probes are designed to withstand no more than about 1000xc2x0 F. As a result, existing combustion dynamic pressure measurement methods do not utilize sensors located directly in the combustion chamber. Rather, current systems use metal tubing called wave guides to transmit the pressure signal from the combustion chamber to a remotely located dynamic pressure sensor. The factors that affect the degree of signal attenuation for these systems include the following:
1. The internal diameter of the tubing.
2. The length of the tubing.
3. The temperature profile within the tubing.
4. The static pressure within the tubing.
5. The frequency content of dynamic pressure signature.
With these systems, a damping coil wound around a horizontal axis is used to prevent the formation of standing waves in the measurement system. This type of system, however, results in the formation of condensate in the horizontal wound damping coil. Condensation build up in the coils results in standing waves being formed in the tubing which attenuates the true source signal and prevents it from being measured accurately. To overcome this problem, current systems have to be periodically purged to remove the condensate from the damping coils.
In addition, the long length of the metal tubing from the combustion chamber to the remotely located sensor results in significant attenuation of the pressure signal, and thus it is not possible to measure the true dynamic pressure of the combustion system with this approach. The signal attenuation resulting from this type of system increases as the frequency of the signal being measured increases.
Accordingly, a probe holder is needed that isolates the dynamic pressure sensor from the temperature of the combustion chamber, while still allowing the sensor to observe in a more accurate manner the dynamic pressure characteristic of the combustion chamber. In other words, this needs to be done in a manner which will not introduce any standing waves, resonances or signal attenuations of the combustion chamber dynamic pressure signals, and that will not result in the formation of condensation in the measurement system.
This invention enables accurate and continuous measurement of the dynamic pressure inside an individual combustion chamber. In the exemplary embodiment, a Tee probe holder is employed that allows the pressure sensor to measure dynamic pressure characteristics in a combustion chamber, without being exposed to the high temperature of the combustion chamber. Specifically, the holder is designed to locate the dynamic pressure sensor in a unique configuration with respect to the pressure signal from the combustion system. In the exemplary embodiment, the Tee probe holder includes a holder body that has a concentric axial bore hole that xe2x80x9ctransmitsxe2x80x9d the combustion chamber dynamic pressure signal to a pressure chamber and pressure sensor that are located in a housing portion of the holder body that is substantially perpendicular to the pressure signal passage.
The pressure signal passage itself extends beyond the pressure sensor and communicates with a metal tube or waveguide having an identical inside diameter that transmits the signal to an acoustic damping system.
The sensing portion of the sensor and an associated diaphragm are sealed within a metal sleeve that is, in turn, supported in the housing portion, with a relatively thin wall separating the sleeve from the pressure sensing passage. An aperture in the wall connects a low volume pressure chamber on one side of the wall, i.e., on the side closest the pressure sensor, to the pressure signal passage.
The forward or sensing portion of the sensor is precision fit within the sleeve, i.e., the sleeve inner diameter and sensor outer diameter are machined to be substantially perfectly round, with a very small clearance that substantially creates a seal between the sleeve and the sensor. In order to allow movement of the sensor diaphragm, however, a larger clearance is provided at the diaphragm by, for example, making the outer diameter of the diaphragm end of the sensor smaller, or by making the inner diameter of the sleeve larger.
O-rings are fitted at each end of the sleeve to attain a substantially perfect seal at opposite ends of the sleeve thereby eliminating any leakage from the pressure chamber.
Mounting of the Tee probe holder in the outer wall of the combustion chamber is achieved using a compression fitting. The depth of the Tee Probe Holder in the combustion chamber is set such that the tip of the probe is flush with the inside of the combustion liner.
In addition, this invention transmits the dynamic pressure signal from the high temperature environment of the combustion chamber via a wave guide to the bottom side of one or more damping coils wound in a helical shape about a vertical axis. The damping coil is made of metal tubing, preferably with the same internal diameter as the metal tubing in the wave guide. The distance from the measurement point to the end of the acoustic damping system (i.e., the remote end of the one or more damping coils) is sufficiently long to insure the signal will be completely damped away before it can reflect and travel back to the measurement point.
By winding the damping coil around a vertical axis, the metal tubing has a continuous downward slope back toward the source of dynamic pressure. As a result, condensation build-up in the system is minimized if not eliminated, since the condensate would simply flow out of the coil under gravity.
In addition, a second passage in the Tee probe holder may extend parallel to the dynamic pressure signal passage and is adapted to open into the radial passage between the outer wall of the combustor and the combustion liner. This passage picks up compressor discharge air and supplies it to the acoustic damping system to further aid in the elimination of any condensation in the attenuation coil where the pressure signal is damped.
The arrangement described above ensures that no standing waves (from condensation), resonances or signal attenuations negatively impact the combustion chamber dynamic pressure signal.
Accordingly, in one aspect, the invention relates to a dynamic pressure probe comprising a holder body having a first passage therein adapted to receive a pressure signal, a pressure sensor including at least a pressure sensing portion located within a sleeve seated within a pressure sensor housing portion, the sleeve engaged with a wall of the housing portion; the pressure sensor including a diaphragm having one face exposed to a pressure chamber within the sleeve between the pressure sensor and the wall; wherein an aperture in the wall of the housing connects the pressure chamber to the first passage; and wherein the first passage continues axially beyond the aperture in a flow direction an acoustic damping coil wound about a vertical axis.
In another aspect, the invention relates to a dynamic pressure probe comprising a holder body having a first passage therein adapted to receive a pressure signal, a pressure sensor including at least a pressure sensing portion located within a sleeve seated within a pressure sensor housing portion, the sleeve engaged with a wall of the housing portion; the pressure sensor including a diaphragm having one face exposed to a pressure chamber within the sleeve between the pressure sensor and the wall; wherein an aperture in the wall of the housing connects the pressure chamber to the first passage; and wherein heating means are provided for raising the temperatures inside the damping coil sufficiently to prevent condensation from forming inside the coil.
In another aspect, the invention relates to a method of obtaining a dynamic pressure signal from a combustor comprising a) supplying a dynamic pressure signal from the combustor through a first passage, the first passage exposed to a mutually perpendicularly arranged sensor diaphragm remote from the combustor; b) transmitting the pressure signal beyond the sensor diaphragm to a signal damping mechanism including a helical coil wound about a vertical axis; and c) supplying compressor discharge air to the signal damping mechanism to remove any condensation therein.